A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and a fuel such as hydrogen or a hydrocarbon-based material such as methanol, ethanol, natural gas, or the like.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC).
The direct oxidation fuel cell includes a direct methanol fuel cell which uses methanol as a fuel.
The polymer electrolyte fuel cell is an environmentally friendly energy source for replacing a conventional energy source. It has advantages such as high power output density, high energy conversion efficiency, operability at room temperature, and the cabability of being down-sized and closely sealed. Therefore, it can be applicable to a wide array of fields such as non-polluting automobiles, residential electricity generation systems, and as portable power sources for mobile equipment, military equipment, and the like.
The fuel cell can be classified as a gas-type fuel cell or a liquid-type fuel cell depending on which kind of fuel is used.
The gas-type fuel cell, which generally uses hydrogen as a fuel, has the advantage of high energy density, but the disadvantage of having to carefully handle hydrogen gas, and also the requirement of accessory facilities, such as a fuel reforming processor, for reforming methane or methanol, natural gas, and the like in order to produce hydrogen as the fuel.
On the contrary, a liquid-type fuel cell, which uses a liquid fuel, has a lower energy density than that of the gas-type fuel cell, but it has the advantages of the ease of handling liquid-type fuel, a low operation temperature, and no need for additional fuel reforming processors. Therefore, it has been acknowledged as an appropriate system for a portable power source for small and common electrical equipment.
In the above fuel cell system, the stack that generates electricity substantially includes several to many unit cells stacked in multiple layers, and each unit cell is formed with a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate).
The membrane-electrode assembly has an anode (also referred to as a fuel electrode or an oxidation electrode) and a cathode (also referred to as an air electrode or a reduction electrode) arranged with an electrolyte membrane between them.
The polymer membrane-electrode assembly is composed of a solid polymer electrolyte membrane and an electrode layer including catalysts supported on carbon. The polymer electrolyte membrane for the electrolyte is commercially available as a perfluorosulfonic acid ionomer membrane such as NAFION™ (by DuPont), FLEMION™ (by Asahi Glass), ASIPLEX™ (by Asahi Chemical), and Dow XUS™ (by Dow Chemical). An electrode layer including catalysts supported on carbon is provided by binding the electrode substrates, such as porous carbon paper or carbon cloth, with carbon powder carrying pulverized catalyst particles such as platinum (Pt) or ruthenium (Ru), using a waterproof binder.
Conventional polymers used in electrolyte membranes for fuel cells have good proton conductivity, but they may have problems including a high cost and low strength. Therefore, there has been a need for a polymer electrolyte membrane having high ion conductivity, high strength, and low cost.